aodv routing protocol

Routing protocols in Adhoc networks

SUBMITTED BY: 13MIT0062

MANET

Mobile adhoc networks

Mobile Ad hoc NET work (MANET) is a self configuring network of mobile routers (and associated hosts)

connected by wireless links – the union of which forms an arbitrary topology

Examples of such networks

Sensor networks Military applications

Sensor networks

Networks deployed in random distribution

Low power Delivering sensor

data to a central site for some purpose

Military applications

Combat regiment in the field Perhaps 4000-8000 objects in

constant unpredictable motion… Intercommunication of forces

Proximity, function, plan of battle

Special issues Low probability of detection Random association and

topology

Dynamic source routing

DSR is designed for MANETs DSR doesn’t need any network infrastructures

Loop free routing No routing information in the intermediate nodes

Nodes may easily cache this routing information for future use

DSR protocol activities

Route discovery

Undertaken when source needs a route

to a destination

Route maintenance

Used when link breaks, rendering

specified path unusable

http://ashrafsau.blogspot.in/

destination

source1

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(1,4)

(1,2)

(1,3)

(1,3,5,6)(1,3,5)

(1,4,7)

source broadcasts a packet containing address of source and destination

The route looks up its route caches to look for a route to destinationIf not find, appends its address into the packet

The destination sends a reply packet to source.

The node discards the packets having been seen


How to send a reply packet

If the destination has a route to the

source in its route cache, use it

Else if symmetric links are

supported, use the reverse of route

record

Else if symmetric links are not

supported, the destination initiates

route discovery to source


Route Maintenance Whenever a node transmits a data packet, a

route reply, or a route error, it must verify that the next hop correctly receives the packet.

If not, the node must send a route error to the node responsible for generating this route header Intermediate nodes “eavesdrop”, adjust

cached routes Source deletes route; tries another if

one cached, or The source restart the route discovery


Route Maintenance……

A B C D E

Route error message: C-D is broken


Disadvantages

Packet header size grows with route length due to source routing.

Flood route request may potentially reach all nodes in the network.

Route reply storm problem.

AODV Overview

AODV is a packet routing protocol designed for use in mobile ad hoc networks (MANET)

Intended for networks that may contain thousands of nodes

Source, destination and next hop are addressed using IP addressing

Each node maintains a routing table that contains information about reaching destination nodes.

Main Features of the AODV Protocol

The Ad hoc On-Demand Distance Vector protocol is both an on-demand and a table-driven protocol.

The packet size in AODV is uniform unlike DSR. Unlike DSDV, there is no need for system-wide broadcasts due to local changes.

AODV supports multicasting and unicasting within a uniform framework.

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Main Features of the AODV Protocol (II)

Each route has a lifetime after which the route expires if it is not used.

A route is maintained only when it is used and hence old and expired routes are never used.

Unlike DSR, AODV maintains only one route between a source-destination pair.

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Routing Table Fields

Destination IP address Destination Sequence Number Valid Destination Sequence Number Flag Other state and routing flags Network Interface Hop Count (needed to reach destination) Next Hop Lifetime (route expiration or deletion time)

Lifetime of a Route-Table Entry

A lifetime is associated with the entry in the route table.

This is an important feature of AODV. If a route entry is not used within the specified lifetime, it is deleted.

A route is maintained only when it is used. A route that is unused for a long time is assumed to be stale.

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Overview Routing table size is minimized by only including

next hop information, not the entire route to a destination node.

Sequence numbers for both destination and source are used.

Managing the sequence number is the key to efficient routing and route maintenance

Overview

The basic message set consists of: RREQ – Route request RREP – Route reply RERR – Route error HELLO – For link status monitoring

Messages

Route Request: “I need a route” Route Response: “Route

advertisement” Route Error: “Withdraw route”

Periodic route response to neighbors acts as “hello”, installing and refreshing route

RREQ Message

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B? B

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Route Requests in AODV

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B

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Represents a node that has received RREQ for D from S

M

N

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B

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JC

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Represents transmission of RREQ

Z

YBroadcast transmission

M

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S

D


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B

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Represents links on Reverse Path

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Reverse Path Setup in AODV

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B

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JC

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• Node C receives RREQ from G and H, but does not forward it again, because node C has already forwarded RREQ once

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B

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B

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• Node D does not forward RREQ, because node D is the intended target of the RREQ

M

N

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Forward Path Setup in AODV

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B

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Forward links are setup when RREP travels alongthe reverse path

Represents a link on the forward path

S

D

RREP Message

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Message routing

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RREQ

RREQ

RREQ

RREQ

RREQ

RREQRREQ

RREQ

RREQ

RREP

RREP

RREP

Source

Destination

Discovery

Broadcast RREQ messages. Intermediate nodes update their routing table Forward the RREQ if it is not the destination. Maintain back-pointer to the originator. Destination generates RREQ message. RREQ sent back to source using the reverse

pointer set upby the intermediate nodes.

RREQ reaches destination, communication starts.

Route Discovery A route between two nodes is

found by sending an Route Request to a locality Initial locality small, grows

with failure After that, a little larger than

the locality target last found in Route Response sent

By target if necessary By neighboring routing node if

possible to “join” existing route

Network stores the routed

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ihg

f

A

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C

B

Route Errors Routes expire if not

refreshed routing nodes log recent

downstream users of a route

When routes expire or are flushed, downstream users are notified to flush

New route request triggeredd

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A

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C

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AODV Routing

There are two phases Route Discovery. Route Maintenance.

Each node maintains a routing table with knowledge about the network.

AODV deals with route table management. Route information maintained even for short lived routes –

reverse pointers.

Maintenance

Hello messages broadcast by active nodes periodically HELLO_INTERVAL.

No hello message from a neighbor in DELETE_PERIOD,link failure identified.

A local route repair to that next hop initiated. After a timeout ,error propagated both to originator and

destination. Entries based on the node invalidated.

Congestion Handling

One method that AODV handle congestion is: If the source node receives no RREP from the

destination, it may broadcast another RREQ, up to a maximum of RREQ_RETRIES.

For each additional attempt that a source node tried to broadcast RREQ, the waiting time for the RREP is multiplied by 2.

DSR is not capable of handling congestion.

Congestion Handling

Other possible methods to improve AODV congestion handling: A route may predict when congestion is about

to occur and try to avoid it by reduce the transmission rate.

Schedule the requests so that it will not overload the network.

Link Failure

A neighbor of node X is considered active for a routing table entry if the neighbor sent a packet within active_route_timeout interval which was forwarded using that entry

Neighboring nodes periodically exchange hello message

When the next hop link in a routing table entry breaks, all active neighbors are informed

Link failures are propagated by means of Route Error (RERR) messages, which also update destination sequence numbers

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Route Error

When node X is unable to forward packet P (from node S to node D) on link (X,Y), it generates a RERR message

Node X increments the destination sequence number for D cached at node X

The incremented sequence number N is included in the RERR

When node S receives the RERR, it initiates a new route discovery for D using destination sequence number at least as large as N

When node D receives the route request with destination sequence number N, node D will set its sequence number to N, unless it is already larger than N

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Security Attacks in AODV 1 Black hole attack2 Message tampering attack3 Message dropping attack

AODV: Summary

Routes need not be included in packet headers

Nodes maintain routing tables containing entries only for routes that are in active use

At most one next-hop per destination maintained at each nodeDSR may maintain several routes for a single

destination

Sequence numbers are used to avoid old/broken routes

Sequence numbers prevent formation of routing loops

Unused routes expire even if topology does not change

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DSR vs AODV

I. Packet header overheadII. Route learning capabilityIII. Handling multiple route repliesIV. ScalabilityV. Security

aodv routing protocol

Engineering